1. Field of the Invention
The present invention relates to a molding machine having squeeze device and rapping device both mounted on an upper part of the machine.
2. Description of the Prior Art
In one type of the prior art molding machines, the movable elements of the machine, such as squeeze device, rapping device and so on, were disposed below a molding table. When sand was introduced into a molding flask placed on the molding table, a part of the sand was apt to be scattered and to fall onto and into the movable machine parts to cause machine troubles and decrease the accuracy of the machine operation. Particularly, the mold forming performance or capability of a molding machine depends greatly upon the accuracy of the rapping device. If the rapping device of a machine is not accurately operative, a pattern cannot easily be removed from a mold formed and a part of the sand forming the mold drops from the mold with a resultant disadvantageous formation of fins on a cast metal. Because of the problem discussed, the rate of the actual operation of the machine and the yield rate of products are greatly decreased.
A deposit is formed on the lower part of a molding machine by the sand which is scattered and falls during a molding operation. If the deposit of sand is not fully swept away or if the machine is not designed to prevent the formation of a deposit of scattered sand, it is possible that the lower part of the machine is embedded in the deposit. Thus, the effect of dropped and scattered sand to a molding machine is not negligible at all.
The normal type of the prior art molding machine was equipped with a squeeze head which was either rotatable in a horizontal plane or generally horizontally movable fore and aft into and out of vertical alignment with a molding flask on a molding table. Because a sand hopper had to be disposed so as not to interfere with the movement of the squeeze head, the bottom end of the hopper was upwardly spaced a substantial distance from the molding flask. It was for this reason that sand falled and scattered onto the lower part of a machine either directly from the hopper or from the molding flask during sand charging operation. It was impossible to completely eliminate this problem. It was also impossible to uniformly supply a molding flask with the minimum and necessary amount of sand. Despite the problems and disadvantages discussed above, many prior art molding machines were each designed such that the movable machine parts, such as squeeze device, rapping device and so on, were disposed below the molding table.
In an attempt to solve the problems and eliminate the disadvantages, it was proposed to dispose in an upper machine section the movable machine parts such as squeeze device, rapping device and so on and to operatively connect the squeeze device with a sand hopper so that the squeeze device and the hopper were alternately reciprocally moved. The molding machine according to the proposal, however, had a shortcoming that the squeeze device and the hopper were heavy-weighted (amounting to several tons in the case of the molding of large-sized molds) had to be reciprocally moved in each molding operation. In order that the machine might be used for a high speed molding, the machine had to be equipped with shock absorbing means and powerful driving means for the heavy-weighted machine components, which inevitably complicated the machine structure and increased the cost of manufacture of the machine. The molding machine of the described type had a further problem that it was difficult to mount a sand-heaping flask which was the conventional means to uniformly charge a molding flask with sand.
Another type of molding machine was proposed in which sand-charging chutes were disposed on the opposite sides of the machine so as not to interfere with a sand hopper and a squeeze head. This type of molding machine, however, necessitated a complicated structure and arrangement to eliminate or avoid interference between the squeeze head and the sand chutes during a squeezing operation.
Moreover, the feeding of sand into a molding flask was carried out generally in such a manner that a batch of sand substantially corresponding to a flask of sand in squeezed condition was fed and held in a sand hopper during the formation of a preceding mold to shorten the time required for each molding operation. After the preceding mold was formed and removed from the machine, an empty molding flask was fed into the machine and the batch of sand was then released and introduced into the empty flask by opening a sand gate disposed above the flask. The gate was formed of a single gate plate or a pair of gate plates or a plurality of rotatable gate plates. In any case, a squeeze head had to be moved to a position above the sand-charged molding flask to perform a squeezing operation. Thus, the molding machine was inevitably large-sized and complicated and, in addition, involved a loss time in each molding operation due to the time required for the reciprocal movement of the squeeze head into and out of vertical alignment with a sand-charged molding flask.
In an attempt to solve this problem, a further type of molding machine was proposed in which a squeeze head was divided into two sections which were laterally reciprocally movable relative to other between separated and united or combined positions so that the time required for one reciprocal movement of the two squeeze head sections was reduced substantially to one half the time required by one reciprocal movement of the single-headed squeeze head. With the further type of molding machine, when the two squeeze head sections were in the separated-apart position, sand was fed into an empty molding flask through the space defined between the separated squeeze head sections. The squeeze head sections were then moved into united or combined position and a molding table was then lifted to upwardly urge the sand in the flask against the united squeeze head sections to squeeze the sand. This type of molding machine, however, necessitated a mechanism for the reciprocal movement of the two squeeze head sections as well as a mechanism for the opening and closing of the bottom of sand hopper. In addition, it was impossible with this type of molding machine to dispose the movable parts of the machine, such as squeeze cylinder, rapping device and so on, in the upper part of the machine because of the structural design of the machine.